The present invention relates to video coding techniques. Typical video distribution systems include at least one video source and at least one receiving device. The video content may be distributed over a network or over fixed media. To keep complexity and cost low, video content is typically limited in dynamic range, e.g., 8-10 bit signal representations and 4:2:0 color format. Recent advances in display technology, however, have opened the door for the use of more sophisticated content (also referred to as “higher quality content”), including content characterized as High Dynamic Range (HDR) and/or wide color gamut (WCG), as well as content with increased spatial and/or temporal resolution. This higher quality content is typically converted to a lower range using a Transfer Function (TF) and color conversion before encoding for distribution using a video codec system. These steps can introduce banding and other artifacts that may impact and substantially degrade the quality of the video content when decoded and displayed.
One technique for improving encoding performance in the context of material available in a higher quality representation when encoded at a lower quality representation is considering original content characteristics during an encoding process. That is, for the motion estimation and mode decision processes, instead of computing distortion in a space native to the encoding space (“native space”), distortion is computed in a “target space” such as an original space or an extended space. By first converting the data to this target space before performing the appropriate computations, the encoding and quality may be improved, i.e., bitrates may be reduced. Video encoding optimization with extended spaces with respect to processes such as intra-mode decision, motion estimation, and mode decision is further discussed in U.S. patent application Ser. No. 14/503,200 filed on Sep. 30, 2014, the entirety of which is incorporated herein by reference.
However, typical techniques do not address in-loop processing mechanisms such as de-block filtering and sample adaptive offset (SAO) filtering. These in-loop processing components may impact the characteristics of a signal in both the native and extended spaces. If extended space optimization is considered only at stages prior to the application of in-loop processes, an “extended space” optimized decision (such as at a motion estimation and/or mode decision stage) may be negated by the in-loop processes.
Therefore, the inventor(s) perceived a need in the art for an improved encoding process that accounts for in-loop processes and is capable of handling higher quality content that results in an improved experience at the decoder compared to conventional encoders, and may reduce banding and blockiness, improve resolution and subjective quality, as well as reduce other artifacts and improve compression.